The invention relates to the improved transport of particulate matter in a wellbore fluid, and particularly concerns the transport of particulate matter in subterranean wells, particularly hydrocarbon wells. The invention especially concerns the removal of particles and particle deposits, such as from drill cuttings, during the drilling of wells, and to the removal of particulate matter deposits in cleanout operations.
Deposition of particulate material in a wellbore, from sources such as formation cuttings or particles transported from a loose structure or fracture, can pose significant problems in the drilling of a well or in subsequent wellbore operations. For example, the deposition of such particles between the drillstring or a coilable drill tubing and the wellbore wall during drilling can interfere with fluid circulation, thereby increasing pumping costs and possibly clogging the wellbore. Again, later-occurring particulate deposits, such as may occur during production of a hydrocarbon fluid, can also clog a wellbore and reduce the rate of production from the well.
While deposition of particulate matter may occur in drilling any wellbore, including vertically drilled wellbores, particulate deposition is a more frequent concern in directional drilling of so-called xe2x80x9cdeviatedxe2x80x9d or curved wellbores. The deviated wellbore may be drilled utilizing conventional drillstring techniques and equipment, or the well may be drilled by specialized tools which are not rotated from the surface but which rely on rotational means positioned downhole. In both instances, as in standard vertical drilling, the drill bit utilized is supplied with a fluid or xe2x80x9cmudxe2x80x9d for lubrication and for removal of formation cuttings as the drilling proceeds. With conventional equipment, the drilling fluid or mud is circulated down the interior of the rotating drill pipe, through and/or around the drill bit, and back up the wellbore to the surface in the annulus formed between the exterior of the drillpipe and the wall of the wellbore. In operations utilizing a downhole driving source, the drilling fluid is commonly sent downhole through a coilable thinner tubing (commonly referred to in the art as coiled tubing) which does not rotate, perhaps through the driving source, and then through and/or around the bit, cuttings and fluid being returned up the wellbore through the wellbore annulus or space between the coiled tubing and the wall of the wellbore.
In both types of operations, i.e., whether with standard equipment or with coiled tubing, the deviated wellbore, with its horizontal component and bends, provides surface locations or sites which are especially susceptible to the deposition of particulate matter, e.g., the cuttings present in drilling fluid, or proppant migrating from a fracture. While drilling fluid pressure is normally sufficient to prevent complete clogging of the well during drilling operations, the resulting increased pressure drop due to the reduced size of the fluid return path represents, as indicated, a significant penalty in terms of pumping requirements. Coiled tubing operations are particularly troubled by particulate deposits because the normal drillstring rotation which tends to keep particles in suspension is not present and the use of the thinner diameter tubing provides extra space in the wellbore for such deposits. In addition, during production operations from a completed well, particle transport from a loose subterranean structure, or even proppant flowback from a fracture, can result in deposits which may block or reduce product flow and ultimately clog the wellbore. In such cases, expensive xe2x80x9ccleanoutxe2x80x9d operations, which involve down time in well production, must be undertaken.
A need, therefore, has existed for provision of an efficient means for preventing or inhibiting, or method of operation for preventing or inhibiting, significant or extended deposition of particles in wellbores, particularly during drilling, more particularly in the drilling of deviated wellbores, and most especially in the drilling of deviated wellbores with coiled tubing. A need has further existed, in the event deposition of particulate matter does occur, for providing an effective xe2x80x9ccleanoutxe2x80x9d means or method for elimination or reduction of the wellbore deposits, whether in drilling operations or in subsequent production operations. The invention addresses these needs.
Accordingly, in one embodiment, the invention relates to a method of inhibiting deposition of particulate matter in a wellbore annulus while drilling a well, such as a well for the production of hydrocarbons, in which a wellbore or drilling fluid is provided to the bit, and a fluid mixture comprising wellbore or drilling fluid and particulate matter is returned through the wellbore annulus to the earth surface, the wellbore or drilling fluid comprising an effective amount of translocating fibers and/or platelets and being provided at a flow rate sufficient to maintain particulate matter and translocating fibers and/or platelets in suspension in the wellbore annulus. According to the invention, in one further aspect of this embodiment, translocating fibers and/or platelets, and particulate matter, are removed from the fluid mixture, while in another approach, particulate matter is removed and fibers and/or platelets containing fluid may be recovered or returned for use. In a further embodiment, the invention relates to a method in which a deposit of particles or particulate matter in a wellbore is contacted with a fluid containing translocating fibers and/or platelets at a rate sufficient to remove and suspend particles from the deposit in the fluid. As utilized herein, the phrase xe2x80x9cparticulate matterxe2x80x9d and the term xe2x80x9cparticlesxe2x80x9d are considered generally synonymous, and refer to discrete solids, such as drillbit cuttings, proppant fragments, or other particles occurring in wellbores. Again, as used herein, the term xe2x80x9ctranslocatingxe2x80x9d, with reference to the fibers and/or platelets employed, refers to the capability of the fibers and/or platelets to assist fluid transfer of particulate matter in the fluid, as well as, in conjunction with wellbore fluid, initiate movement of such particulate matter in the fluid from a deposit in the wellbore. Translocating fibers and/or platelets, therefore, will be of sufficient size and stiffness as to exert a mechanical force individually or in aggregation as a network on particles in the wellbore fluid or in deposits thereof such that the particulate matter is assisted or maintained in suspension in the fluid or its suspension therein is promoted. In a further embodiment, the invention relates to a method of drilling a well, preferably a well for the production of hydrocarbons, in which a wellbore is drilled with a drill bit while supplying or providing a suitable wellbore or drilling fluid to the bit, the fluid comprising or containing an effective amount of translocating fibers. The drilling operation produces or forms a fluid mixture comprising the wellbore or drilling fluid, particulate matter (or cuttings), and the translocating fibers, in the wellbore. In the usual case, the wellbore fluid mixture is circulated out of the wellbore and the particulate material and fibers are subsequently removed from the fluid mixture, leaving a fluid which may be reused. Optionally, and depending, inter alia, on the translocating fibers employed, the particulate material may be removed, and the fibers and fluid may be reused. In yet a further embodiment, the invention relates to a method or process in which a wellbore or cleanout fluid, such as a drilling fluid or a well treatment fluid, and containing translocating fibers, is provided to or circulated in a wellbore containing deposited particulate matter. After contacting the deposit, the wellbore fluid containing particulate matter removed from the deposit is returned to the surface. Particulate material and fibers may be removed from this wellbore fluid mixture, leaving a wellbore fluid which may be recovered or reused, or particulate matter may be removed, leaving a fibers-containing fluid which may be recovered or reused. In additional embodiments, translocating platelets may be used instead of fibers, and mixtures of translocating fibers and platelets may also be used. As will be apparent, the invention is particularly and uniquely adapted to the drilling of and cleanout of deviated wells, especially those such operations in which coiled tubing is employed. While there is no desire to be bound by any theory of invention, evidence suggests, as indicated, that the presence of an appropriate quantity of fibers, and/or platelets, of the type described, in a circulating fluid, aids transport of particles. Additionally, evidence also suggests that during circulation of the described fibers-containing fluid over or in contact with deposits of particulate material, the fibers promote or assist in removal or detachment and transport of particles from the deposits and in maintaining particles in the fluid. The intent of the invention, therefore, is to utilize the fibers and/or platelets in active wellbore operations such as drilling and wellbore cleanout, the fibers and/or platelets being maintained in suspension in the wellbore annulus and generally without significant aggregation during use. In each instance, as employed herein, the phrase xe2x80x9cand/orxe2x80x9d is used to indicate that the terms or expressions joined thereby are to be taken together or individually, thus providing three alternatives enumerated or specified.